1. Field of the Invention
The present invention relates to a displacement control device for a variable displacement compressor in an automotive air conditioning system, and more particularly, to a device which controls the discharge capacity of such variable displacement compressors in accordance with such air conditioning systems.
2. Description of Related Art
Variable displacement compressors having capacity control devices are known in the art. For example, Japanese First Patent Publication (Unexamined) No. 7-346845, which is incorporated herein by reference, describes a variable displacement compressor having a displacement control device in an automotive air conditioning system. In such automotive air conditioning systems, the compressor is driven by an engine of a vehicle without a clutch, e.g., an electromagnetic clutch.
This clutchless variable displacement compressor has a capacity control device, a discharge chamber, a crank chamber, a swash plate, a drive shaft, and a communication passage, which communicates between the crank chamber and the discharge chamber. The swash plate is provided on the drive shaft within the crank chamber. The capacity control device has a valve member, which is operated by an electromagnetic solenoid and opens or closes the communication passage for controlling refrigerant gas flowing from the discharge chamber to the crank chamber. Therefore, pressure within the crank chamber may be controlled, and a tilt angle between the swash plate and the drive shaft also may be controlled. As a result, the capacity control device of this compressor may control the discharge capacity of the variable displacement compressor.
When the automotive air conditioning system is switched off, this compressor may be operated in a minimum discharge capacity by the capacity control device. Even when the automotive air conditioning system is switched on, this compressor may be properly operated at a minimum discharge capacity by the capacity control device to maintain a predetermined temperature of a compartment of a vehicle.
In the capacity control device of such compressors, if the automotive air conditioning system is switched off for a long time, e.g., a few months, this compressor may be operated at the minimum discharge capacity by the capacity control device for a long time. e.g., a few months. In this operation, the tilt angle between the swash plate and the drive shaft becomes a maximum value, and stirring lubricant oil by the swash plate may be reduced. Therefore, circulation of refrigerant gas in a refrigerant circuit may be reduced, and the lubricant oil, which is discharged to the refrigerant circuit, may not return to this compressor. As a result, stirring the lubricant oil by the swash plate may be gradually reduced, and this compressor may become scored or cracked.
Moreover, in a capacity control device of a known variable displacement compressor of an automotive air conditioning system, the known variable displacement compressor alternatively may be driven by an engine of a vehicle via a clutch, e.g., an electromagnetic clutch. If such a compressor is continually operated in a minimum discharge capacity operation under the control of the capacity control device, problems similar to those encountered in the known clutchless, variable displacement compressor may occur.
A need has arisen to reduce or eliminate the above-mentioned defects or damages, which may be encountered in known variable displacement compressors with capacity control devices.
In an embodiment of this invention, there is provided a device for controlling a discharge capacity of a variable displacement compressor for use in an automotive air conditioning system of a vehicle. The air conditioning system comprises the compressor and an evaporator fan. The device comprises a control, a first detector, and a second detector. The control means adjust the discharge capacity of the compressor between a minimum discharge capacity and a maximum discharge capacity. The first detector means detect an elapsed time of minimum discharge capacity operation of the compressor. The second detector means detect an impressed voltage of the evaporator fan of the air conditioning system. The discharge capacity increases from the minimum discharge capacity to a predetermined discharge capacity when the elapsed time of the minimum discharge capacity operation is greater than a predetermined time and when the impressed voltage of the evaporator fan is greater than a predetermined voltage.
In another embodiment of this invention, there is provided a method for controlling a discharge capacity of a variable displacement compressor for use in an automotive our conditioning system of a vehicle. The air conditioning system has the compressor and an evaporator fan. The method comprises the steps of decreasing the discharge capacity of the compressor from a maximum discharge capacity to a minimum discharge capacity, detecting an elapsed time of a minimum discharge capacity operation of the compressor, detecting an impressed voltage of the evaporator fan of the air conditioning system, and adjusting the discharge capacity from the minimum discharge capacity in response to a comparison between the detected values and predetermined values corresponding to the detected values.
Objects, features, and advantages of embodiments of this invention will be apparent to persons of ordinary skill in the art from the following detailed description of the invention and the accompanying drawings.